The invention relates to a process for producing cooling gas for a producer gas produced in a melt-down gasifier and surplus gas usable in an appropriate manner by cooling and cleaning at least part of the producer gas and the top gas of an iron ore reduction unit, the cooling gas being obtained exclusively from the producer gas.
German Pat. No. 30 34 539 discloses a process for directly producing molten pig iron from lump iron ore, which is reduced in a direct reduction shaft furnace to sponge iron by means of reducing gas and is then melted in a melt-down gasifier with the aid of coal and oxygen-containing gas and simultaneously the producer gas used for reducing the iron ore is produced. This is cooled and the dust removed threefrom and then a first partial flow thereof is blown into the reducing zone of the direct reduction shaft furnace. A second partial flow is cooled and washed again for producing cooling gas for the producer gas. The top gas obtained in the direct reduction shaft furnace is removed at its upper end and supplied for appropriate uses, it normally being worked up in a cooling and cleaning unit separate from the producer gas circuit. These units are subject to widely varying operating conditions both for the producer gas and for the top gas. In normal operation, almost the entire producer gas produced in the melt-down gasifier is used as reducing gas and also the cooling gas quantity can be very small, so that no or little surplus gas, not required for operational purposes and emanating from the producer gas is obtained. On starting up the apparatus operating according to the known principle, as well as during different operating faults, most of the producer gas is guided via the cooling and cleaning unit for the cooling gas, whereas the top gas quantity is very small. Thus, fluctuations occur with regards to the gas quantities passed through the particular washer up to a ratio of approximately 1:20. However, the control range of the washer used extends over a quantity ratio of up to approximately 1:4. In the case of quantity fluctuations exceeding this ratio, it is therefore not possible to maintain the operation of the apparatus and the admissible clean gas dust contents. A regulation of the quantity changes to approximately 1:20 can possibly be obtained if each cleaning unit was equipped with two adjustable Venturi washers or scrubbers and the associated drop separators. However, this would lead to other difficulties, particularly the risk of frequent obstruction or clogging due to the considerable dust quantities carried in the gases.
The problem of the present invention is therefore to improve the known process for producing cooling gas for producer gas produced in a melt-down gasifier and surplus gas usable in an appropriate manner by cooling and cleaning at least part of the producer gas and the blast furnace gas of an iron ore reduction unit, the cooling gas being obtained exclusively from the producer gas, in such a way that with considerable fluctuations of the gas quantities supplied to the cooling and cleaning units it is always possible to drop the dust content to the desired values of e.g. 5 to 10 mg/Nm.sup.3, the maintenance of such units being simple and inexpensive, whilst their energy consumption is also relatively low.